1 1st PUMP HANDS-ON MAINTENANCE AND RELIABILITY CONFERENCE Session 1 CENTRIFUGAL PUMPS ATLANTA, GA SEPTEMBER 22-23, 2005 2Centrifugal pumps Head generators Positive Displacement pumps Flow generators 3CENTRIFUGAL 4Lets Get to the Hardware! 5(No Transcript) 6PERFORMANCE CURVE - COMBINEDMax ODNPSHR linesEfficiency linesBestEfficiencyPoint lineMCSF lineBHP linesRated pointMin. OD 7AFFINITY LAWSWhat happens to Flow, Head and Power with Speed? Flow changes DIRECTLY (linear) with RPM Head changes as a SQUARE of RPM Power is proportional to Flow times Head it changes as CUBE of RPM Q RPM H RPM2 BHP RPM3 8More Affinity LawsWhen impeller OD is trimmed Flow, Head and Power follow the Affinity Laws very similar to the case of speed changeODoldQ x H x2 BHP x3ODnewwhere x is a cut ratio x ODnew /ODold(Note additional correction applies for cuts over 10) 9Lets test some pumps! 10a SYSTEM CURVESystem Hydraulic LossesFriction (hf)hf V2/2gStatic (h0)Flow 11Parallel OperationHeadFlow500500x2 1000 12Double the pumps - But will Flow Double for sure?! 13It depends on a System!1000 ft (static head) long pipe, elbows, valves a lot of frictionCase BCase A 14Case A mostly static headHead, fth0 1000 ftFlow, gpm500500x2 1000 15Case B mostly frictionIf the system can not handle it more pumps will not add any more flow!Head, ftFlow, gpm1000 500550 !? 16SUCTION CHARACTERISTICSCAVITATION, NPSHBasically, if there is not enough pressure liquid boils! 17In your kitchen, the water boils at 100 oC (212 o F) and that is at atmospheric pressureIf pressure drops, the water will boil at lower pressureOn top of high mountain water boils at perhaps 95 oC ? 18NPSH DEFINITIONNPSHA available NPSHR requiredNPSHA is a total available suction pressure - over the vapor pressure - (expressed in feet of head). In other words, it is Net Suction Head minus vapor pressure (expressed as head)NPSHA is NOT simply the level of liquid in the suction tank 19A lot of bubblesMore bubblesIncipientHead, ft3NPSHR3NPSHA, ft 20NPSHRWith suction pressure dropping, a point may be reached that liquid starts to transform into vapor somewhere inside the pump. This is not good. But how bad is bad?Hydraulic Institute define the NPSHrequired as such value of NPSHR when a pump losses 3 of its developed head. They call this NPSHR3 For simplicity, they just write it as NPSHR, implying 3 21CAVITATION DAMAGEToo many candies makes kids hyper. But it also ruins their teeth. 22Impeller inlet blades cavitation on a suction sideAs bubbles flow from low pressure to higher, they implode against metal surfaces. These micro-hammer-like impacts erode the material, creating cavities thus cavitation 23

Good ways to fight suction problems

Make sure a pump is as close to suction source as possible

For double-suction pumps, suction valve stem should be oriented for symmetrical feed flow

Smaller eye impeller (lower suction specific speed) can help

Inlet sump design critical vortexing and air entrapment could be a nightmare

Metallurgy 316ss stainless work-hardens, while iron does not very long

27Single Mechanical Seal, multiple springs, unbalanced (Courtesy Durametallic) 28Double Mechanical Seal, multiple springs, unbalanced (Courtesy Durametallic) 29(Courtesy Durametallic) 30(Courtesy Durametallic) 31MAG-DRIVE PUMPS(Courtesy of Goulds Pumps) 32Pumps and Systems Reliability 33Types of Misalignment 34Effect of Water on Bearing LifeOne PPM is one milligram per kilogram. 35Pump-to-Piping AlignmentStep 1 Pre-installation stage (pump may not have even arrived to site yet) anchor the main piping properly. Leave room for the final spool pieces (to be made later) by the pump. 36Step 2 Rough alignment phase. Pump has arrived. Position it and make spool pieces. 37Step 3 Remove all equipment. Level the baseplate to 0.025 from end to end. Clean up and get ready for the grouting. 38Step 4 Grouting phase. 39Step 5 Reinstall the pump and a motor on a baseplate. Inspect and make sure nothing is binding up. 40Step 6 Rough align pump to a motor. 41Step 7 Make up final spool pieces. 42Step 8 Install the spool pieces between piping and a pump. Leave gaps (1/16 1/8) for the gaskets. This gap is the only distance the piping will be pulled during final bolting, and stresses will be minimal. (The pump will thank you for that). 43Step 9 Final alignment of a motor to pump. 44Step 10 Final piping verification. Unbolt the pump from the driver. Loosen up piping bolts and retighten. Indicator should not move more then 0.002. Otherwise modify, adjust or remake spool pieces. 45Pumps Troubleshooting

Startups

Troubleshooting

Repair and Overhaul

Note of acknowledgment is due to my friend Mr.. Jim Brennan of IMO/Colfax, and his excellent articles on pumps startup, troubleshooting and overhaul, published in Pumps Systems magazine over the years. Jim has over 30 years experience in the pump industry, and is active in various pump committees and organizations. Much of this information was based on his recommendations, as well as our numerous and continued discussions and friendly debates over the years. 46Startups

Most vulnerable time for pumps

Read technical manuals and instructions thoroughly

Pump

Driver

Auxiliaries

Review piping and valving first

Backwards?

Absent?

No weld beads, no weld rods, no scale

Temporarily strainers

Permanent strainers

Clean start conditions

47Startups cont.

Was piping pressure tested? Design limits observed?

Low pressure air to find gasket leaks

Check and tighten flange bolts to correct values

Is inlet piping straight for long enough distance?

Is piping adequately supported? Is your pump condemned to be an anchor?

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